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The title gave me a weird idea... Photosynthesising plants dont convert the entire spectrum of light to energy. What if u had a filter that turned all the sunlight into the wavelength that the plant uses, could u get more food from the same area of land?

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I don't think we currently know of any practical way to _arbitrarily_ change the wavelength and frequency of electromagnetic waves (within the same medium), and even if there was, it would likely take so much energy that it would never be efficient to spend the energy this way.

Somehow submerging the plants within a different medium to change the entire spectrum would also likely not achieve any gains either, because by doing that you can only reduce the total amount of energy in any part of the spectrum, not shift it elsewhere (afaik).

edit: added 'arbitrarily' - as replies point out, moving towards the lower-energy end of the spectrum is not hard.

Fluorescence is pretty easy and cheap, we use it all the time. Yellow fluorescent material is added to blue LEDs to make white LEDs; blue fluorescent material is added to paper, clothing, and laundry detergent to make whites appear brighter under UV light.

Shifting frequency the other direction is much harder; some materials exist that can double the frequency of light (known as second harmonic generation), but it's not as cheap as fluorescence. They are used in green laser pointers to turn infrared light into green light.

> I don't think we currently know of any practical way to change the wavelength and frequency of electromagnetic waves (within the same medium), and even if there was, it would likely take so much energy that it would never be efficient to spend the energy this way.

Isn't this the entire principle behind using quantum dots in displays?

i.e. The quantum dots absorb light from the backlight and then re-emit it as a very specific color band.

What? Yes we do. It's called fluorescence.

If you find a color range not being used effectively, it's easy to drop the frequency down to a better one.

Sorry, I should have written 'practical way to arbitrarily change...'. One of the sibling comments to yours touches on the topic of increasing the frequency, which is what I was getting at with the practicality and energy consumption.

That is exactly what solar panel scientists want to achieve, but it’s very hard to actually do. Capturing more of the spectrum is what’s let the efficiency percentage slowly creep from the 20’s into the 30’s.

Photosynthesis is ca. 2% to 5% effective while even common off the shelf PV panels reach 20% easily. Assuming an efficient light source in the desired spectral range that'd make it more efficient to grow plants under solar panels with such light sources using the generated power than growing them under glass or out in the open.

Physical materials(Filters here) can change the wavelength but not the frequency. So it's still the same UV/light band. You can't change that.

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